Alkylation process

ABSTRACT

This invention relates to a process for the alkylation of aromatics by reacting an aromatic hydrocarbon with an olefin in the presence of an ionic liquid comprising (a) a compound of the formula R n  MX 3-n  wherein R is a C1-C6 alkyl radical, M is aluminium or gallium, X is a halogen atom and n is 0, 1 or 2 and, (b) a hydrocarbyl substituted imidazolium halide or a hydrocarbyl substituted pyridinium halide wherein at least one of the said hydrocarbyl substituents in the imidazolium halide is an alkyl group having 1-18 carbon atoms. The process allows ready separation of reaction products from the ionic liquid and improves selectivity to alkylated products.

This application is a continuation of application Ser. No. 08/513,810,filed Sep. 5, 1995, now abandoned, which is a 371 of PCT/GB95/00254,filed on Feb. 9, 1995.

FIELD OF THE INVENTION

This invention relates to process for the alkylation of aromatichydrocarbons using an ionic liquid as catalyst.

BACKGROUND OF THE INVENTION

Alkylation of aromatics is well known in the art and is usually carriedout by the reaction of an alkyl halide with an aromatic hydrocarbon inthe presence of a Lewis acid catalyst such as hydrofluoric acid, borontrifluoride, concentrated sulphuric acid, zeolites and combinationsthereof. More recently, acidic catalysts such as aluminium halides andthe alkyl aluminium halides have been preferred, optionally incombination with a co-catalyst such as an alkyl halide. For instance,styrene has been produced by the catalytic dehydrogenation of ethylbenzene which in turn is derived by direct alkylation of benzene withethylene in the presence of such a catalyst. Such alkylation processesare described in detail by eg Olah, G A., ed. Friedel-Crafts and RelatedReactions, Interscience Publishers, J Wiley & Sons, New York (1964) andby Streitweiser, A and Reif, L., J Am Chem Soc 82, 5003 (1960). Theseprocesses use two reactors of which one is a so-called "primaryalkylator" and the other is a so-called "trans- or de-alkylator". Bothreactors are constructed from acid resistant materials eg Hastalloy®B orfuran-lined firebrick in a 316 SS casing. Ethylene and benzene are fedinto the primary alkylator in mole ratios in the range of 0.1:0.9. Acatalyst complex is formulated eg by adding aluminium powder to benzenein the presence of ethyl chloride (which combination represents thepromoter and catalyst) and small quantities of polyethylbenzenes. A `redoil` catalyst complex is thus generated which is then fed into theprimary alkylator in an amount which is <1% w/w of the total reactantsin the primary alkylator. The `red oil` is fed to the primary alkylatorsuch that it totally dissolves in the benzene/ethylene system. Theresultant mixture is subjected to controlled reaction conditions suchthat the effluent from the primary alkylator contains a mixture ofunreacted benzene, ethyl benzene (the desired product), and by-productsincluding diethyl benzene and polyethyl benzenes. This effluent streamis combined with recycled polyethyl benzenes in the trans-alkylator. Thecontents of the trans-alkylator, which are liquids, reach a compositionwhich may or may not be thermodynamically controlled depending uponcatalyst activity. Invariably, the effluent from the trans-alkylatorwill be different in composition from the primary alkylator as it willcontain less benzene and more of the desired ethyl benzene. The effluentfrom the trans-alkylator is washed with water and alkali, eg sodiumhydroxide or ammonia to destroy the catalyst. This means that that thecatalyst is irretrievably lost and cannot therefore be recycled orreused. The washed material is then distilled to produce benzene forrecycle, the desired ethyl benzene, di- and tri-ethyl benzenes forrecycle and the remaining heavy materials such as tetra-, penta- andhexa-ethyl benzenes and impurities are recovered and used as `flux oil`.The ethyl benzene is recovered and kept in a suitable storage facilityeg in tanks, until required for the dehydrogenation stage to producestyrene.

Such catalysts have the disadvantage that some of the acids used such ashydrofluoric acid are too strong, corrosive and volatile and thereforerequire a considerable degree of safety measures both for the equipmentused and for the operational personnel involved; others such asconcentrated sulphuric acid are relatively inactive and require highreaction volumes and expensive reconcentration equipment; and zeolitesare too weak therefore requiring the use of relatively high reactiontemperatures. Where aluminium halides are used, they are usuallymiscible with the reactant hydrocarbons and have to be destroyed torecover the desired alkylated product thereby preventing recycle of thecatalyst and hence adding to the cost of the process.

Alkylation of isoparaffins by olefins has also been reported inFR-A-2626572 in the presence of a catalyst comprising ionic liquids.This document, however, does not describe the alkylation of aromaticsusing olefins. The process of alkylation of iso-paraffins is differentfrom that involving the alkylation of aromatics because, surprisingly,these catalysts for the alkylation of iso-paraffins--where relativelysevere reaction conditions are required to obtain the desired specieswith high octane rating--can also catalyse the alkylation of aromaticswith the desired conversion-selectivity.

Ionic liquids are primarily mixtures of salts which melt below roomtemperature. Such salt mixtures include aluminium halides in combinationwith one or more of imidazolium halides, pyridinium halides orphosphonium halides and the latter being preferably substituted.Examples of the latter include one or more of 1-methyl-3-butylimidazolium halides, 1-butyl pyridinium halide and tetrabutylphosphonium halides.

It has now been found that aromatic hydrocarbons can be alkylateddirectly with olefins without recourse of alkyl halides as thealkylating agent whilst at the same time mitigating the problemsgenerated by the use of strong acids, expensive equipment or inabilityto recycle the catalysts used as described above.

SUMMARY OF THE INVENTION

Accordingly, the present invention is a process for the alkylation ofaromatics by reacting an aromatic hydrocarbon with an olefin in thepresence of an ionic liquid comprising

(a) a compound of the formula R_(n) MX_(3-n) wherein R is a C1-C6 alkylradical, M is aluminium or gallium, X is a halogen atom and n is 0, 1 or2 and,

(b) a hydrocarbyl substituted imidazolium halide, a hydrocarbylsubstituted pyridinium halide or mixtures thereof

wherein at least one of the said hydrocarbyl substituents in theimidazolium halide is an alkyl group having 1-18 carbon atoms.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The hydrocarbyl substituted imidazolium halide or a hydrocarbylsubstituted pyridinium halide is suitably selected from 1-alkyl-3-alkylimidazolium halides and 1-alkyl pyridinium halides. Specific examples ofthese compounds include the following:

1-methyl-3-ethyl imidazolium chloride,

1-ethyl-3-butyl imidazoliium chloride,

1-methyl-3-butyl imidazolium chloride,

1-methyl-3-butyl imidazolium bromide,

1-methyl-3-propyl imidazolium chloride,

1-methyl-3-hexyl imidazolium chloride,

1-methyl-3-octyl imidazolium chloride,

1-methyl-3-decyl imidazolium chloride,

1-methyl-3-dodecyl imidazolium chloride,

1-methyl-3-hexadecyl imidazolium chloride,

1-methyl-3-octadecyl imidazolium chloride,

1-methyl-3-hexyl-imidazolium chloride,

1-methyl-3-octyl-imidazolium chloride,

1-methyl-3-decyl-imidazolium chloride,

1-methyl-3-dodecyl-imidazolium chloride,

1-methyl-3-hexadecyl-imidazolium chloride,

1-methyl-3-octadecyl-imidazolium chloride,

ethyl pyridinium bromide,

ethyl pyridinium chloride,

ethylene pyridinium dibromide,

ethylene pyridinium dichloride,

butyl pyridinium chloride and

benzyl pyridinium bromide.

The imidazolium halides of the present invention can be prepared by anyof the well known methods described in the art especially thosedescribed eg in FR-A-2626572. In the case of the imidazolium halideswhich have more than 5 carbon atoms in the alkyl substituent, thefollowing method may be used for synthesis thereof:

For instance, a 1-alkyl-3-methyl imidazolium halide can be prepared bymixing dry 1-methylimidazole with 1-alkyl haloalkane (and optionallywith a solvent such as eg acetonitrile, if a homogeneous mixture isdesired) and placing them eg in a Corius tube inside a dry box. TheCorius tube is then closed using a super seal in the dry box and sealedunder vacuum. The two components form two layers inside the Corius tubeand the resulting mixture is then heated to about 100° C. for about aweek. The resultant product is then cooled to room temperature to form aviscous product which is then transferred from the dry box to a Schlenkround bottomed flask and left under vacuum for a few hours. Theresultant viscous liquid is then analysed for identification andcharacterisation of the 1-alkyl-3-methyl imidazolium halide.

The ionic liquids of the present invention contain, in addition to theimidazolium halides and/or pyridinium halides defined above, analuminium or gallium compound which is suitably an aluminium halide orgallium halide such a aluminium trichloride or gallium trichloride, or,an alkyl aluminium/gallium halide such an alkyl aluminium/galliumdichloride or a dialkyl aluminium/gallium halide and is preferably ethylaluminium/gallium dichloride.

It is well understood in the art that the ratio of the components in anionic liquid used as catalyst should be such that they remain in aliquid state under the reaction conditions. When preparingmulti-component ionic liquids, the presence of the imidazolium halideshaving more than 5 carbon atoms in the alkyl group enables such liquidsto tolerate a higher proportion of the other component(s) and stillremain liquids, in some cases at room temperature, than is possible withconventional imidazolium halides.

The present invention can also be carried out by using as catalyst anionic liquid which comprises a ternary melt of:

(a) a compound of the formula R_(n) MX_(3-n) wherein R is a C1-C6 alkylradical, M is aluminium or gallium, X is a halogen atom and n is 0, 1 or2,

(b) at least one of a hydrocarbyl substituted imidazolium halide and ahydrocarbyl substituted pyridinium halide, and

(c) at least one of a hydrocarbyl substituted quaternary ammonium and ahydrocarbyl substituted phosphonium halide.

The compound (a) in the ternary melt is suitably an aluminium halide,such as aluminium trichloride, a gallium halide such as galliumtrichloride, or, an alkyl aluminium/gallium halide such as an alkylaluminium/gallium dihalide or a dialkyl aluminium/gallium halide, and ispreferably ethyl aluminium/gallium dichloride.

The component (b) in the ionic liquid is a hydrocarbyl-substitutedimidazolium halide or a hydrocarbyl substituted pyridinium halide. Thesemay be suitably selected from the list described above. The component(c) in the ternary melts is a hydrocarbyl-substituted quaternaryammonium halide or a hydrocarbyl-substituted phosphonium halide. Of thesubstituent groups in the ammonium halides at least one substituent isan alkyl group. The other substituents may be the same or differentgroups selected from hydrogen, alkyl, aryl, aralkyl and alkaryl groups.Similarly, the hydrocarbyl substituted phosphonium halides contain atleast one hydrocarbyl group. The other substituents may be the same ordifferent groups selected from hydrogen, alkyl, aryl, aralkyl andalkaryl groups. Specific examples of such compounds include inter aliatetra-alkyl ammonium halides or tetra-alkyl phosphonium halides in eachof which the alkyl group suitably has 1-20, preferably 1-18 and morepreferably from 1-6 carbon atoms.

The relative ratios of components (a), (b) and (c) in the ternary meltis suitably that they are capable of remaining in the liquid state underthe reaction conditions. Typically, the relative mole ratio of component(a) to the components [(b)+(c)] in the ternary melt ionic liquid issuitably in the range from 1:2 to 3.0 :1, preferably from 1.5:1 to 2:1.Within this range, where the ionic liquid is intended for use as areaction medium or a solvent, the amount of the component (a) can beless than 50 mole % of the total ionic liquid. However, where the ionicliquid is intended for use as a catalyst, the amount of component (a) ispreferably greater than 50 mole % of the total ionic liquid. Therelative mole ratios of (b):(c) in such an ionic liquid is suitably inthe range from 0.01:1 bearing in mind that within this range the ratioschosen should be such that the resultant ionic liquid is a liquid atroom temperature.

The ternary melts of the present invention are suitably prepared bymixing the components in an atmosphere inert under the reactionconditions for binary mixtures as described in our publishedEP-A-0558187. It is preferable to purify each of the components in themelt prior to preparing the melt. Thus, aluminium trichloride can bepurified by repeated sublimations until the melt at the bottom of thesublimator is clear and the aluminium trichloride takes on a lustrous,shiny appearance; the hydrocarbyl substituted imidazolium or pyridiniumhalides can be purified by repeated recrystallisations from solutionsthereof in a suitable solvent; and the hydrocarbyl substitutedquaternary ammonium or phosphonium halide can be purified by dissolvingthe halide in a suitable solvent such as eg ethanol and precipitation ofthe halide from the ethanol solution by dilution with eg diethyl etherfollowed by filtration and drying in an inert atmosphere.

The olefins that may be used for the alkylation reaction are suitablyC2-C10 olefins, preferably the lower olefins, eg the C2-C4 olefins,particularly ethylene, propylene and the butenes.

The aromatic hydrocarbons that can be alkylated by the process of thepresent invention are suitably monocyclic such as eg benzene andtoluene, although bi-cyclic and poly-cyclic aromatics such asnaphthlenes can also be alkylated.

The mole ratio of olefin to the aromatic hydrocarbon used for thealkylation reaction is suitably in the range from 0.1 to 0.9, preferablyfrom 0.3 to 0.7 and more preferably from 0.4 to 0.6.

The alkylation reaction is suitably carried out temperature in the rangefrom 80 to 200° C., preferably from 100 to 170° C., and at a reactionpressure in the range from 0.5 to 3.0 MPa, preferably from 1.0 to 2.4MPa. However, it will be known to those skilled in the art that thereactor pressure will be dependent upon the temperature due to thevapour pressure of the aromatic hydrocarbon and the desire to achieve aset olefin to aromatic hydrocarbon ratio within the ranges described.

The alkylation reaction is suitably carried out in an atmosphere inertunder the reaction conditions such as eg nitrogen.

The ionic liquid catalyst is suitably used in an amount from 0.1 to 1.0%w/w, preferably from 0.2 to 0.5% w/w based on the total weight of thehydrocarbon reactants in the reaction mixture.

The ionic liquid catalyst may be supplemented by a co-catalyst such aseg an alkyl halide. The alkyl group in the alkyl halide is suitably suchthat it corresponds to the olefin used for alkylation of the aromatichydrocarbon. Examples of the alkyl halides that may be used includeethyl chloride and tertiary butyl chloride.

The use of ionic liquids as alkylation catalysts have the followingadvantages over the conventional catalysts. They:

i. readily form a separate phase from the other components of thereaction mixture due to their polar nature, acidity and density, therebyenabling recycle of the catalyst unlike conventional catalysts which areirretrievably destroyed prior to the recovery of the alkylated productfrom the reaction mixture;

ii. improve the selectivity to the alkylated product and hence improvethe efficiency of the alkylation process; and

iii. can be readily produced with a greater degree of control duringmanufacture unlike the conventional catalysts which suffer from theproblems of variability of composition; this in turn ensures a greaterdegree of control of the alkylation process and leads to a smoother andmore economic operation of the liquid phase alkylation process.

ILLUSTRATIVE EXAMPLES AND COMPARATIVE TESTS

The present invention is further illustrated with reference to thefollowing Examples and comparative tests. In the Examples relating tothe preparation of the uncommon alkyl imidazolium halides, the1-methylimidazole used was distilled over sodium hydroxide and wasalways handled under a cover of nitrogen. The alkyl halides used wereall dried over calcium hydride for a week and then distilled prior touse. It is not believed that any detailed analysis of these compounds isnecessary in order to ascertain their structure since the reactions arestoichiometric, no gases are evolved nor any solids deposited during thereaction. However, in order to prove that this is the case, ¹ H NMRanalyses has been carried out on the products from some of the Examplesand on this basis a structure has been assigned for those products onwhich no NMR analyses have been carried out.

In Tables below, the intensity referred to is the peak height whichcorresponds to the number of protons in that position. In this respectthe notations very strong, strong, medium and weak represent thefollowing range of peak intensities (I/Io):

    ______________________________________                                        very strong     80-100                                                          strong  60-80                                                                 medium  40-60                                                                 weak  20-40                                                                   very weak <20                                                                 δ (ppm) chemical shift in parts per million                           ______________________________________                                    

EXAMPLES

A. Preparation of Imidazolium halides

A1. Preparation of 1-pentyl-3-methyl Imidazolium Chloride

Dry 1-methylimidazole (9.03 g, 0.11 mol) was mixed with 1-chloropentane(10.66 g, 0.1 mol) in a Schlenk round bottomed flask. The two componentsformed two layers, and acetonitrile (40 ml) was added to make themixture homogeneous. The mixture was heated under reflux, under cover ofdry nitrogen, for 5 hours. The resultant solution was allowed to cool toroom temperature and evaporated to dryness in vacuo. The solid so formedwas redissolved in acetonitrile (20 ml) and cooled to -13° C. for 5days. This resulted in the formation of crystals which were isolated bySchlenk filtration and dried in vacuo for 48 hours. The yield of1-pentyl-3-methyl imidazolium chloride was 8.2 g (69.9%), had a meltingpoint of 58.2° C., m/z of 341. An ¹ H NMR spectrum of the product ofthis Example A1 is shown below in Tables 1 and

                  TABLE 1                                                         ______________________________________                                        Conventional C.sub.1 /C.sub.2 Melt NMR of a Product containing                  65 mole % of AlCl.sub.3 (for comparison)                                      δ (ppm)   Intensity (I/IO)                                                                         Type                                             ______________________________________                                        1.1           strong     doublet                                                3.4 very strong singlet                                                       3.8 weak triplet                                                              6.8 weak doublet                                                               7.85 weak doublet                                                          ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        C.sub.1 /C.sub.5 Melt NMR of a Product containing                               65 mole % of AlCl.sub.3                                                       (Example A1)                                                                  δ (ppm)   Intensity (I/IO)                                                                         Type                                             ______________________________________                                        0.5           very strong                                                                              singlet                                                1.0 very strong singlet                                                       1.5 medium singlet                                                            3.5 very strong singlet                                                       3.8 medium singlet                                                            6.9 medium doublet                                                            7.9 medium singlet                                                          ______________________________________                                    

A2. Preparation of 1-hexyl-3-methyl Imidazolium Chloride

Dry 1-methylimidazole (9.03 g, 0.11 mol) was mixed with 1-chlorohexane(12.06 g, 0.1 mol) and placed in a Corius tube inside a dry box. TheCorius tube was then closed using a super seal in the dry box and sealedunder vacuum. The two components formed two layers, inside the Coriustube, and this mixture was heated at 100° C. for a week. The resultingproduct was allowed to cool to room temperature when it formed a viscousproduct. The viscous product was transferred from the dry box to aSchlenk round bottomed flask where it was left under vacuum for 4 hoursto form a viscous liquid.

This liquid was not analysed by ¹ H NMR but the structure is that shownby analogy with that in Example A1 above. The product was a liquid atroom temperature and the yield was 12.23 g (92.2%) with an m/z value of369.

A3. Preparation of 1-octyl-3-methyl Imidazolium Chloride

The process of Example A2 above was repeated except that 1-chlorooctane(14.9 g, 0.1 mol) was used instead of 1-chlorohexane. The viscous liquidwas not analysed by ¹ H NMR but by analogy with Example A1 , thestructure is that shown. The product was a liquid at room temperature,the yield was 15.8 g (96.6%) and had an m/z value of 425.

A4. Preparation of 1-nonyl-3-methyl Imidazolium Chloride

The process of Example A2 was repeated except that 1-chlorononane (16.3g, 0.1 mol) was used instead of 1-chlorohexane. The viscous liquidproduct was not analysed by ¹ H NMR but was assigned the structure shownby analogy with Example A1. The product was a liquid at roomtemperature, the yield was 16.1 g (90.0%) and had an m/z value of 453.

A5. Preparation of 1-decyl-3-methyl Imidazolium Chloride

The process of Example A2 was repeated except that 1-chlorodecane (17.7g, 0.1 mol) was used instead of 1-chlorohexane. The viscous liquidproduct was not analysed by ¹ H NMR but was assigned the structure shownby analogy with Example A1. The product was a liquid at roomtemperature, the yield was 18.3 g (94.2%) and had an m/z value of 481.

A6. Preparation of 1-dodecyl-3-methyl Imidazolium Chloride

The process of Example A2 was repeated except that 1-chlorododecane(20.48g 0.1 mol) was used instead of 1-chlorohexane. The product uponheating at 100° C. was waxy and was recrystallised from acetonitrile (50ml) at -13° C. for a week in a Schlenk round bottomed flask. Thecrystals were isolated by Schlenk filtration and dried in vacuo for 48hours. The ¹ H NMR analysis of the crystals is shown in Table 3 below.The crystals had a melting point of 52.5° C., the yield was 19.4 g(86.1%) and had an m/z value of

                  TABLE 3                                                         ______________________________________                                        C.sub.1 /C.sub.12 Melt NMR of a Product containing                              40 mole % of AlCl.sub.3                                                       (Example A6)                                                                  δ (ppm)   Intensity (I/IO)                                                                         Type                                             ______________________________________                                        0.5           weak       singlet                                                0.9 very strong doublet                                                       1.5 very weak singlet                                                         3.5 weak singlet                                                              3.8 very weak singlet                                                         4.6 very weak singlet                                                         5.3 very weak singlet                                                         7.0 very weak singlet                                                         8.0 very weak singlet                                                       ______________________________________                                    

A7. Preparation of 1-tetradecyl-3-methyl Imidazolium Chloride

The process of Example A6 was repeated except that 1-chlorotetradecane(23.3 g 0.1 mol) was used instead of 1-chlorododecane. The crystalsformed were not analysed by ¹ H NMR but were assigned the structureshown by analogy with Example A6. The crystals had a melting point of56.89° C., the yield was 23.9 g (93.3%) and had an m/z value of 593.

A8. Preparation of 1-hexadecyl-3-methyl Imidazolium Chloride

The process of Example A6 was repeated except that 1-chlorohexadecane(26.09 g 0.1 mol) was used instead of 1-chlorododecane. The crystalswere not analysed by ¹ H NMR but were assigned the structure shown byanalogy with Example A6. The crystals had a melting point of 61.6° C.,the yield was 25.7 g (89.6%) and had an m/z value of 649.

A9. Preparation of 1-octadecyl-3-methyl Imidazolium Chloride

The process of Example A6 was repeated except that 1-chlorooctadecane(28.9 g 0.1 mol) was used instead of 1-chlorododecane. The crystals werenot analysed by ¹ H NMR but the structure was assigned on the basis ofanalogy with Example A6. The crystals had a melting point of 71.07° C.,the yield was 31.77 g (93.3%) and had an m/z value of 705.

B. Preparation of Ternary Melt Catalysts

B1. Purification of Aluminium Trichloride

In an inert-atmosphere box, anhydrous aluminium trichloride (ca. 200 g)was placed in a sublimator with sodium chloride (2 g) and powderedaluminium (1 g). The apparatus was transferred to a vacuum line wherethe mixture was heated in vacuo in a silicone oil-bath, to 150° C. Thealuminium trichloride was left to sublime until ca. 10% of it remainedat the bottom of the sublimator together with the molten NaCl andimpurities. After cooling, the apparatus was placed back into theinert-atmosphere box where the sublimed AlCl₃ was removed by scrapingand then placed again into a clean apparatus with NaCl (2 g) forre-sublimation. (Powdered aluminium was utilized in the firstsublimation only, to remove iron impurities). Five successivesublimations were carried out until the melt observed at the bottom ofthe sublimator was clear and the AlCl₃ took on a lustrous, shinyappearance.

B2. Preparation of 1-ethyl-3-methylimidazolium chloride

The preparation was carried out in a fume cupboard. The apparatuscomprised a round-bottomed flask provided with an additional funnel andwas adapted to be heated to elevated temperature. The apparatus waspurged clean with nitrogen and the reaction was carried out undernitrogen. 1-Methylimidazole (300 ml), which had previously beendistilled in vacuo over KOH, was placed in the flask under nitrogen.Acetonitrile (ca. 150 ml, distilled over CaH₂) was then added to theflask. The mixture was then heated slowly in small increments until theinternal temperature of the flask was 68° C. and then allowed tostabilize for one day. The nitrogen purge was then replaced with astream of ethyl chloride which was administered through a flow meter atthe rate of 2 dm³ ethyl chloride per hour for two days. Thereafter, theflow of ethyl chloride was reduced to 1 dm³ per hour and maintained atthis rate for a further three days. After this duration, a solutioncontaining the desired product was removed from the flask whilst stillhot by cannula and this solution was extracted with ethyl acetate andsmall white crystals of 1-ethyl-3-methylimidazolium chloride wererecovered from the extract. Further purification was carried out byrecrystallisation from further aliquots of ethyl ethanoate.

B3. Purification of Tetra-Ethylammonium Chloride

Tetra-ethylammonium chloride (100 g) was dissolved in ethanol (150 ml).Diethyl ether was then added to this solution until tetra-ethylamoniumchloride started to precipitate. The solution was cooled to -13° C. andleft at this temperature overnight. The resulting crystals were filteredunder dry nitrogen and then heated in a Schlenk round bottomed flask to100° C. under vacuum for 48 hours. The resulting solid was thentransferred to a dry box ready to use.

B4. Preparation of Ternary melt

Crystalline 1-ethyl-3-methylimidazolium chloride was melted in vacuo andpoured into an aluminium foil "boat" under an inert atmosphere and thenallowed to soldify therein. The solid so formed was then broken intolarge lumps. These lumps were then reacted with lumps of tetraethylammonium chloride and aluminium trichloride in varying quantities andunder conditions shown in the Table 4 below to prepare six differentbatches (Batch Nos. 1-6) of acidic and basic melts. Lumps were usedinstead of powders to prevent charring of the melt during heating.

                  TABLE 4                                                         ______________________________________                                        Batch                             Ternary                                                                             AlCl.sub.3                              No. [Et.sub.4 N]Cl (g) [MeEtim]Cl (g) AlCl.sub.3 Melt (g) (Moles)           ______________________________________                                        1    0.8922 (23.333%)                                                                          0.3936 (11.66%)                                                                           2.0  3.287 0.65                                    2 0.6958 (17.5%) 0.5922 (17.5%) 2.0 3.288 0.65                                3 1.2428 (40%) 0.5498 (20%) 1.0 2.793 0.40                                    4 0.6214 (20%) 1.0996 (40%) 1.0 2.721 0.40                                    5 0.3107 (10%) 1.3745 (50%) 1.0 2.680 0.40                                    6 0.1553 (5%) 1.512 (55%) 1.0 2.667 0.40                                    ______________________________________                                         [Et.sub.4 N] is tetraethylammonium chloride                                   [MeEtim]Cl is 1ethyl-3-methylimidazolium chloride                             Ternary Melt is [Et.sub.4 N]/[MeEtim]Cl/AlCl.sub.3                       

The ternary melts were characterised using ¹ H NMR spectroscopy byplacing the neat ionic liquid in a 4 mm diameter NMR tube in vacuo. Nosolvent was used for the analysis. The results of the analysis aretabulated in Tables 5 (standard melt) 6 and 7 (ternary melt) below:

                  TABLE 5                                                         ______________________________________                                        .sup.1 NMR of Standard Binary C.sub.1 /C.sub.2 Melt for Comparison              δ (ppm)   Intensity (I/IO)                                                                         Type                                             ______________________________________                                        1.0           strong     triplet                                                3.4 very strong triplet                                                       3.8 medium doublet                                                            6.9 medium doublet                                                            7.8 medium singlet                                                          ______________________________________                                         C.sub.1 /C.sub.2 Melt  Stendard melt & methyl & ethyl imidazolium             chlorides                                                                

                  TABLE 6                                                         ______________________________________                                        .sup.1 NMR of Ternary Melt (65% AlCl.sub.3,                                     23.3% [Et.sub.4 N]Cl & 11.7% [MeEtim]Cl)                                      δ (ppm)   Intensity (I/IO)                                                                         Type                                             ______________________________________                                        0.7           very strong                                                                              singlet                                                1.0 weak singlet                                                              2.6 very strong singlet                                                       3.3 medium singlet                                                            3.7 weak doublet                                                              4.6 very weak singlet                                                         6.8 very weak doublet                                                         7.8 very weak singlet                                                       ______________________________________                                         [Et.sub.4 N]Cl  tetra ethyl ammonium chloride                                 [MeEtim]Cl  1ethyl-3-methyl imidazolium chloride                         

                  TABLE 7                                                         ______________________________________                                        .sup.1 NMR of Ternary Melt (40% AlCl.sub.3,                                     15% [Et.sub.4 N]Cl & 45% [MeEtim]Cl)                                          δ (ppm)   Intensity (I/IO)                                                                         Type*                                            ______________________________________                                        1.0           very strong                                                                              singlet                                                2.8 very weak singlet                                                         3.5 very strong singlet                                                       3.8 strong singlet                                                            7.4 medium singlet                                                            9.2 weak singlet                                                            ______________________________________                                         *  all peaks were broad peaks                                                 [Et.sub.4 N]Cl tetraethyl ammonium chloride                                   [MeEtim]Cl  1ethyl-3-methyl-imidazolium chloride                         

C. Alkylation Using Ionic Liquids as Catalyst

The apparatus used for this Example was a Buchi autoclave (5 litrecapacity) system made from 316 stainless steel. The autoclave was fittedwith a temperature control jacket containing silicone oil heat transferliquid and, electronic temperature and pressure measurement devices. Theautoclave was also fitted with magnetically driven `U`-shaped paddlestirrer (0-2000 rpm). The autoclave was connected to pressurisedethylene and nitrogen supplies. A catalyst injection system wasincorporated into the nitrogen supply to the autoclave.

The autoclave was charged with benzene (500 ml, SpectrophotometricGrade, ex Aldrich Cat. No. 15,546-8) at room temperature and was thenpressurised with ethylene (ex Air Products) to 1.7 MPa. The fluidsinside the autoclave were then stirred at 200 rpm. Some of the ethylenedissolved in the benzene thereby producing a pressure drop which wasrecorded. The autoclave was topped up with more ethylene to 1.4 MPa.

The temperature of the autoclave was then raised to 105° C. When asteady temperature and pressure were attained, an ionic liquid catalystcomprising (a) 67% w/w aluminium trichloride and 33% w/w1-ethyl-3-methyl-imidazolium chloride (10 ml, equivalent to 13.2 g) and(b) ethyl chloride (1.0 ml) was injected into the autoclave undernitrogen. The nitrogen pressure was set to 0.01 MPa above the recordedsteady state autoclave pressure.

Since the reaction was instantaneous, ethylene pressures were recordedas a function of residence time after catalyst injection. Periodically,samples of the liquid reaction mixture were removed from the autoclaveand analysed by Gas Chromatography using a Phillips PU 4500chromatograph fitted with a CPSIL 5 column to separate benzene, ethylbenzene, diethyl benzene and heavier materials. The data from the GC wascomputed to arrive at the conversion, selectivity and yield data as afunction of residence time. The reaction was allowed to continue untilequilibrium was achieved as determined by a steady yield when thereaction was considered to be complete. Upon completion, the catalystwas allowed to settle into a separate phase from the liquid reactionproducts. The reaction products were then analysed using standard atomicabsorption techniques. The results are tabulated below.

Comparative Test (Not According to the Invention)

In a comparative test, a conventional catalyst was used instead of theionic liquid. The conventional catalyst was manufactured by adding ethylbenzene (200 ml, ex Aldrich 29,684-8) to aluminium trichloride (20 g,99% purity) and ethyl chloride (1.0 ml) in a pre-dried glass container.The resultant slurry was agitated by shaking and allowed to stand. A`red oil`, catalyst complex as described above was formed at thesolid-liquid interface. This catalyst complex was removed and storedunder nitrogen.

The alkylation apparatus and procedure used was exactly the same as thatfor Example B above except the catalyst used was the complex `red oil`(10 ml) prepared as above injected together with ethyl chloride (1.0ml). The results are tabulated in Table 8 below:

                  TABLE 8                                                         ______________________________________                                                           Ionic Liquid                                                                            Red Oil                                            Reaction Conditions Catalyst Catalyst                                       ______________________________________                                        C.sub.2 H.sub.4 :benzene (Mol Ratio)                                                             0.6       0.6                                                Reaction Temperature (° C.) 110 110                                    Initial Pressure (MPa) 2.4 2.4                                                Stirrer speed (rpm) 2000 2000                                               ______________________________________                                    

The detailed conditions and product analyses are tabulated below foreach of the reactions described above. In Tables 9 and 10 below, thefollowing abbreviations have been used:

    ______________________________________                                        Bz                 Benzene                                                      EtBz Ethyl Benzene                                                            DEB Diethyl Benzene                                                           Conv. Conversion                                                              Sel. Selectivity                                                              By-Prod Heavy By-Products                                                     Res Time Residence Time                                                     ______________________________________                                    

                  TABLE 9                                                         ______________________________________                                        Ionic Liquid Catalyst                                                           Res Time Bz Conv. EtBz Sel.                                                                            EtBz    DEB Sel.                                                                             By-Prod                               (s) (wt %) (%) Yield (%) (%) Sel. (%)                                       ______________________________________                                         300   14.84    80.18    11.89   11.92   7.90                                    600 20.75 77.07 15.99 14.41  8.52                                             900 26.05 73.82 19.23 16.33  9.85                                            1800 33.30 66.88 22.27 18.30 14.82                                            3600 38.42 63.48 24.39 20.32 16.20                                            5400 40.35 62.86 25.30 20.77 16.37                                            8100 44.33 57.72 25.56 20.48 22.00                                            10800  44.8  57.13 25.56 20.91 21.96                                        ______________________________________                                    

                  TABLE 10                                                        ______________________________________                                        Red Oil Catalyst                                                                Res Time Bz Conv. EtBz Sel.                                                                            EtBz    DEB Sel.                                                                             By-Prod                               (s) (wt %) (%) Yield (%) (%) Sel. (%)                                       ______________________________________                                         180    1.50    41.42     0.62    8.62  49.96                                    360 15.45 71.72 11.08 15.06 13.22                                             600 25.78 68.20 17.58 16.61 15.19                                             960 27.74 68.15 18.91 17.09 14.76                                            1800 34.45 58.96 20.30 16.59 24.45                                            3000 35.14 61.05 21.45 17.89 21.06                                            5700 36.62 62.46 22.87 19.30 18.24                                            9060 41.91 56.92 23.86 19.38 23.70                                            12660  43.85 53.06 23.27 18.21 28.72                                        ______________________________________                                    

We claim:
 1. A process for the alkylation of aromatics by reacting anaromatic hydrocarbon with an olefin in the presence of an ionic liquidcatalyst composition comprising(a) a compound of the formula R_(n)MX_(3-n) wherein R is a C1-C6 alkyl group, M is aluminum or gallium, Xis a halogen atom and n is 0, 1 or 2, and (b) at least one compoundselected from the group consisting of a hydrocarbyl substitutedimidazolium halide, a hydrocarbyl substituted pyridinium halide, and amixture thereof,wherein at least one of the hydrocarbyl substituents inthe imidazolium halide is an alkyl group having 1-18 carbon atoms.
 2. Aprocess according to claim 1 wherein the hydrocarbyl substitutedimidazolium halide or a hydrocarbyl substituted pyridinium halide isselected from 1,3-dialkyl imidazolium halides and 1-alkyl pyridiniumhalides.
 3. A process according to claim 2 wherein at least one of thealkyl substituents in the dialkyl imidazolium halide has 5-18 carbonatoms.
 4. A process according to claim 1 wherein hydrocarbyl substitutedimidazolium or pyridinium halide is selected from the group consistingof:1-methyl-3-ethyl imidazolium chloride, 1-ethyl-3-butyl imidazoliumchloride, 1-methyl-3-butyl imidazolium chloride, 1-methyl-3-butylimidazolium bromide, 1-methyl-3-propyl imidazolium chloride,1-methyl-3-hexyl imidazolium chloride, 1-methyl-3-octyl imidazoliumchloride, 1-methyl-3-decyl imidazolium chloride, 1-methyl-3-dodecylimidazolium chloride, 1-methyl-3-hexadecyl imidazolium chloride,1-methyl-3-octadecyl imidazolium chloride, 1-methyl-3-hexyl-imidazoliumchloride, 1-methyl-3-octyl-imidazolium chloride,1-methyl-3-decyl-imidazolium chloride, 1-methyl-3-dodecyl-imidazoliumchloride, 1-methyl-3-hexadecyl-imidazolium chloride,1-methyl-3-octadecyl-imidazolium chloride, ethyl pyridinium bromide,ethyl pyridinium chloride, ethylene pyridinium dibromide, ethylenepyridinium dichloride, butyl pyridinium chloride and benzyl pyridiniumbromide.
 5. A process according to claim 1 wherein the ionic liquidcomprises a ternary melt of:(a) a compound of the formula R_(n) MX_(3-n)wherein R is a C1-C6 alkyl radical, M is aluminium or gallium, X is ahalogen atom and n is 0, 1 or 2, (b) at least one of a hydrocarbylsubstituted imidazolium halide and a hydrocarbyl substituted pyridiniumhalide, and (c) at least one of a hydrocarbyl substituted quaternaryammonium and a hydrocarbyl substituted phosphonium halide.
 6. A processaccording to claim 5 wherein component (c) in the ternary meltscomprises at least one of tetra-alkyl ammonium halides and tetra-alkylphosphonium halides in each of which the alkyl group suitably has 1-20,preferably 1-18 and more preferably from 1-6 carbon atoms.
 7. A processaccording to claims 5 or 6 wherein the relative mole ratios ofcomponents (a), (b) and (c) is such that the ratio of component(a):[(b)+(c)] in the ternary melt ionic liquid is in the range from 1:2to 3.0:1 and the ratios of (b) : (c) in the range from 0.01:1, so thatthe resultant ionic liquid is a liquid at room temperature.
 8. A processaccording to claim 1 wherein the olefins used for the alkylationreaction are C2-C10 olefins.
 9. A process according to claim 1 whereinthe aromatic hydrocarbons that can be alkylated are monocyclic,bi-cyclic or poly-cyclic aromatics.
 10. A process according to claim 9wherein the aromatic hydrocarbons being alkylated are selected frombenzene, toluene and naphthlenes.
 11. A process according to claim 1wherein the mole ratio of olefin to the aromatic hydrocarbon used forthe alkylation reaction is in the range from 0.1 to 0.9.
 12. A processaccording to claim 1 wherein the alkylation reaction is carried out at atemperature in the range from 80 to 200° C. and at a reaction pressurein the range from 0.5 to 3.0 MPa.
 13. A process according to claim 1wherein the alkylation reaction is carried out in an atmosphere inertunder the reaction conditions.
 14. A process according to claim 1wherein the ionic liquid is used in an amount from 0.1 to 1.0% w/w basedon the total weight of the hydrocarbon reactants in the reaction mixtureto catalyse the alkylation reaction.
 15. A process according to claim 1wherein the ionic liquid is supplemented by an alkyl halide co catalyst.16. A process according to claim 15 wherein the alkyl halide is ethylchloride and tertiary butyl chloride.